Process of recovering valuable metal

ABSTRACT

A method for recovering a valuable metal including the steps of: recovering valuables from scraps containing the valuable metal; and removing at least part of carbon contained in the recovered valuables by heating the valuables in a non-oxidizable atmosphere, and a method for recovering a valuable metal including the steps of: thermally treating a melted mixture including the valuable metal and slag with a flux component to separate the valuable metal in a liquid phase from the slag in another liquid phase. In accordance with the present invention, the valuable metal in the scrap can be easily recovered.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to a method for conveniently and less expensively recovering a valuable metal, and more in detail to the method for recovering the valuable metal from a scrap material including the valuable metal such as nickel, cobalt and rare earth metals in a scrapped nickel-hydrogen secondary cell.

[0003] (b) Description of the Related Art

[0004] As a means for recovering the valuable metal from a scrap material including the valuable metal such as nickel, cobalt and rare earth metals in a scrapped nickel-hydrogen secondary cell, a method is disclosed in JP-A-9(1997)-82371 which includes steps of separating coarse particles (plastics iron and foamed nickel) from fine particles (nickel hydroxide and hydrogen- storing alloy) by crushing the scrapped nickel-hydrogen secondary cell followed by filtration, dissolving the fine particles with sulfuric acid containing an alkali metal to form a cobalt-containing nickel solution, removing impurities therefrom, and recovering the nickel metal and a nickel-cobalt alloy. However, the step of the recovering the valuable metal such as the nickel is quite complicated.

[0005] In the valuable metal recovery from the scrap including the valuable metal, the reduction of the carbon content in the recovered metal must be performed thereby broadening the usage thereof, in addition to the increase of the recovery yield and the simplification of the recovery process. The reduction of the carbon after the recovery requires an undesirable additional step requesting further time and cost.

[0006] In JP-A-2000-67935, a method for recovering valuables from a scrapped nickel-hydrogen secondary cell is disclosed which includes the steps of crushing the scrapped nickel-hydrogen secondary cell, filtrating the valuables in the crushed cell, thermally treating the valuables in an oxidizable atmosphere, and thermally melting the valuables in a reducing atmosphere to provide a melted metal. Carbon in the valuables is removed by the oxidation in the thermal oxidation step.

[0007] However, in the method, although the carbon content in the valuables is reduced in the thermal oxidation step conducted in a higher temperature, the valuable metals such as nickel, cobalt and rare earth metals are simultaneously oxidized. Accordingly, the method is not an effective process for recovering the valuable metals.

[0008] In the conventional method for recovering the valuable metal, the carbon contained in the scrapped nickel-hydrogen secondary cell remains in the valuable metals after the recovery. When the content of the carbon in the valuable metals is reduced, the valuable metals are oxidized. Therefore, the desired valuable metals cannot be obtained.

[0009] Even when the carbon is effectively removed from the valuable metals recovered in this manner, the recovered valuable metals frequently contain slag initially contained in the scraped cell. The slag irremovable by a simple separation procedure is a bar to the recycle of the recovered valuable metals.

SUMMARY OF THE INVENTION

[0010] In view of the foregoing, an object of the present invention is to provide a method for recovering a valuable metal with reduced carbon content without substantial oxidation of the valuable metal, and another method for separating the valuable metal from slag.

[0011] The present invention provides, in a first aspect thereof, a method for recovering a valuable metal including the steps of: recovering valuables from scraps containing the valuable metal; and removing at least part of carbon contained in the recovered valuables by heating the valuables in a non-oxidizable atmosphere (hereinafter referred to as “first invention”).

[0012] In accordance with the first invention, the valuable metals with higher quality and the lower carbon content can be recovered without oxidizing the valuable metals by a thermal treatment of the recovered valuables containing the carbon and oxygen in the non-oxidizable atmosphere.

[0013] The present invention provides, in a second aspect thereof, a method for recovering a valuable metal including the steps of thermally treating a melted mixture including the valuable metal and slag with a flux component to separate the valuable metal in a liquid phase from the slag in another liquid phase (hereinafter referred to as “second invention”).

[0014] In accordance with the second invention, though the melted mixture of the valuable metals and the slag is hardly separated from each other by the conventional separation method, the melted mixture is separated into the heavier melted metal and the lighter melted slag by addition of, with heating, the flux component such as boron oxide and boron oxide+calcium oxide, thereby recovering the valuable metal having the higher purity in a liquid-liquid separating manner.

[0015] The present invention provides, in a third aspect thereof, a method for recovering a valuable metal including the steps of; recovering valuables from scraps containing the valuable metal and slag; removing at least part of carbon contained in the recovered valuables by heating the valuables in a non-oxidizable atmosphere to provide a melted mixture including the valuable metal and the slag; and thermally treating the melted mixture with a flux component to separate the valuable metal in a liquid phase from the slag in another liquid phase (hereinafter referred to as “third invention”).

[0016] In accordance with the third invention, the valuable metal in the scraps can be recovered by utilizing the combined procedures of the first and second inventions.

[0017] The above and other objects, features and advantages of the present invention will be more apparent from the following description.

BRIEF DESCRIPTION OF DRAWINGS

[0018]FIG. 1 is a flowchart showing a method of the present invention which is applied to recovery of valuable metals in a scrapped nickel-hydrogen secondary cell.

PREFERRED EMBODIMENTS OF THE INVENTION

[0019] Now, the present invention is more specifically described.

[0020] The method of the first invention is characterized by the removal of the carbon in the recovered valuable metals without substantially oxidizing the valuable metals by thermally treating the valuables recovered from the scrap containing the valuable metals in the non-oxidizable atmosphere. After the carbon-removing step, the melting step may be added in which the de-carbonized valuable metal is heated for melting.

[0021] The scrap containing the valuable metals includes a scrapped nickel-cadmium cell and a scrapped lithium ion cell in addition to the scrapped nickel-hydrogen secondary cell.

[0022] The valuable metals recovered in this manner usually contain slag originating from the starting cell. The second invention implements the separation of the valuable cells from the slag. The object for the separation in the second invention is not restricted to that from the scrapped material but includes metals containing slag in an ordinary refining process.

[0023] The “valuables” in the present invention refers to composition containing the valuable metal to be recovered and occasionally refers to the recovered valuable metals.

[0024] Then, an example of the present invention for recovering valuable metals in a scrapped material will be described referring to FIG. 1 showing the recovery of valuable metals in a scrapped nickel-hydrogen secondary cell.

[0025] A valuables recovering step may be performed similarly to the conventional valuables recovering method When the scraps containing the valuable metals are the scrapped nickel-hydrogen secondary cell, the cell is crushed by using a shearing machine, is broken into pieces in a wet condition and is classified by using a sieve. After the non-classified substances remaining on the sieve are subjected to the magnetic screening for removing non-magnetized substances such as plastics and paper, small amounts of the plastics and paper are removed by burning.

[0026] Further, when the cell includes foamed nickel as an electrode plate, the electrode plate may be reduced in hydrogen or thermally treated in an inert gas atmosphere for recovering the valuables.

[0027] The valuables obtained in this manner include materials recovered from a negative electrode mainly containing nickel and materials recovered from a positive electrode mainly containing a hydrogen-storaging alloy, and further include an organic binder and a specified amount of carbon.

[0028] Then, the valuables physically classified in this manner are thermally treated in the non-oxidizable atmosphere to oxide at least part of only the carbon, thereby removing the oxidized carbon or carbon monoxide and carbon dioxide (carbon-removing step).

[0029] The non-oxidizable atmosphere refers to an atmosphere in which carbon can be removed by oxidation without substantially oxidizing a metal and an alloy by means of heating and is selected from the group consisting of an inert gas atmosphere, a hydrogen gas atmosphere, a vapor atmosphere, an inert gas-vapor atmosphere and an inert gas-vapor-hydrogen gas atmosphere. The inert gas includes argon, nitrogen and helium, and the preferable non-oxidizable atmosphere is the hydrogen gas atmosphere.

[0030] The heating in the carbon-removing step may be conducted preferably at 350 to 1050° C. for 5 minutes to 10 hours and more preferably at 400 to 750° C. for 30 minutes to 5 hours. The heating below 350° C. cannot take place the condensation dehydration reaction of a metal compound such as nickel hydroxide contained in the valuables and lowers the recovery yield due to the slow reaction rate. The heating above 1050° C. cannot significantly increase the treating efficiency and lowers the energy efficiency of the metal recovery.

[0031] The thermal treatment in the inert gas atmosphere attributes to the reductive or the oxidative removal of the at least part of the carbon by means of oxygen, hydrogen and vapor contained in the recovered valuables, and simultaneously reduces part of a deteriorated metal oxide to the corresponding metal.

[0032] At least part of the carbon in the valuables is reduced in the hydrogen atmosphere to lower hydrocarbons to be removed from the valuables.

[0033] In the vapor atmosphere, at least part of the carbon in the valuables is denaturated or oxodized with the vapor to be removed from the valuables.

[0034] After at least part of the carbon in the valuables is removed in the carbon-removing step, the valuables are converted into the valuable metal which is then recovered as the cool solid metal upon the stopping of the heating in the carbon-removing step.

[0035] Some of the metals are preferably recovered as the melted metal depending on the usage. In such a case, the metals after the carbon-removing step are heated continuously with the heating of the carbon-removing step or are re-heated after the stop of the heating of the carbon-removing step, thereby recovering the valuable metals as the melted metals (melting step). The melting step is not indispensable.

[0036] The atmosphere for the heating in the melting step is preferably an inert gas atmosphere such as argon for suppressing the oxidation of the valuable metals.

[0037] In the method of the present invention including the above requirements, the carbon-removing step in the inert gas atmosphere effectively utilizes the hydrogen and the oxygen contained in the scrap containing the valuable metals can remove at least part of the carbon contained in the scrap without substantially oxidizing the metals easily oxidized such as Misch metal.

[0038] The carbon-removing step in the hydrogen gas atmosphere reductively removes at least part of the carbon contained in the scrap by means of the hydrogen contained in the atmosphere without substantially oxidizing the metals easily oxidized such as Misch metal.

[0039] The carbon-removing step in the vapor atmosphere removes at least part of the carbon contained in the scrap by means of the oxidation or denaturation without substantially oxidizing the metals easily oxidized such as Misch metal.

[0040] The carbon-removing step conducted in this manner does not substantially accompany the oxidation and reduces the carbon content in the valuables to 1000 ppm (0.1% in weight) or less or to 100 ppm (0.01% in weight) or less depending on conditions.

[0041] Although the carbon in the recovered valuables can be easily removed by the conventional oxidation treatment, the treatment further oxidizes the other metal components such as nickel, cobalt and the Misch metal, thereby requiring additional vast energy for reducing the oxidized metals to lower the efficiency.

[0042] On the other hand, the carbon-removing step in the present invention enables the carbon removal in the valuables without accompanying the oxidation of the metal components to require no additional step for reducing the scrap and enables the simple recovery of the valuable metals from the scrap.

[0043] In the ordinary operation, slag originating from the scrap is contained in the recovered valuable metal. Accordingly, the valuable metal after the carbon-removing step is a mixture between the metal and the slag.

[0044] Then, a flux component is added to the thus obtained mixture in the third invention, and to the thus obtained mixture or a separately obtained mixture of this kind in the second invention. In the second invention, the flux component may be added to the solid mixture followed by the melting or to the melted mixture.

[0045] The flux component has a function of separating the melted valuable metals from the melted slag, and is preferably selected from metal compounds usually metal oxides which have melting points around that of the valuable metals. Preferable flux component includes born oxide (B₂O₃), the boron oxide+calcium oxide (CaO), the boron oxide+magnesium oxide (MgO) and the boron oxide+lithium oxide (LiO). An amount of the flux component is preferably 5 to 100% in weight with respect to the total amount of the valuables and the slag, and more preferably 10 to 50% in weight.

[0046] When the mixture containing the flux component is maintained in the melted state, the mixture are subjected to liquid-liquid separation or divided into the melted metal having a larger specific gravity and the melted slag having a smaller specific gravity. Accordingly, the valuable metal having the higher purity can be recovered rather simply.

[0047] When the valuable metal is recovered from the valuables containing the Misch metal oxide (MmOx), for example, the valuable metal cannot ordinarily be separated unless the valuables are heated to the melting point of the Misch metal, for example, to the melting point of lanthanum oxide, that is, to 2310° C. However, the addition of the flux component such as B₂O₃ to converts the Misch metal into MmOx—B₂O₃, having the melting point of about 1300° C. The liquid-liquid separation of the valuable metal can be achieved by heating the mixture to this melting point. When the boron oxide is used as the flux component for the valuable metal recovery, only the valuable metals other than the Misch metal are recovered because the Misch metal is converted into the MmOx—B₂O₃ which is then included in the slag as mentioned before.

[0048] Although the boron oxide itself is preferably used with respect to the valuable metal recovery, the higher activity of the boron oxide make take place the following reaction depending on the conditions.

Mm+B₂O₃→MmOx+B

[0049] The liberated boron may be mixed into the recovered valuable metals as an impurity. The combination of the boron oxide and the calcium oxide suppresses the activity of the boron and prevents the mixing of the boron into the valuable metal.

[0050] As mention before, the valuable metal with the slag having the reduced amount of the carbon can be recovered from the scrap in accordance with the first invention by using the carbon-removing step.

[0051] The mixture containing the metal and the slag can be separated by using the flux component in accordance with the second invention.

[0052] The valuable metal in the scrap can be recovered by using the valuables-recovering step, the carbon-removing step and the valuable metal-recovering step in accordance with the third invention.

EXAMPLES

[0053] Although Examples of the method for recovering the valuable metals of the present invention will be described, the present invention shall not be deemed to be restricted thereto.

Valuables Recovering Step

[0054] A scrapped nickel-hydrogen secondary cell was dry-crushed by using a shearing machine (Rotoplex Cutting Mill made by Alpine A.G. of Germany). The crushed cell was wet-broken into pieces by using an attriction machine, the broken pieces were then classified by using a sieve (28 mesh). After the non-classified substances remaining on the sieve are subjected to the magnetic screening at 2000 to 3000 Gauss for removing non-magnetized substances such as plastics and paper, small amounts of the plastics and paper are removed by burning. The residue after the burning was crushed by using a vibration mill (“T-100 Type” available from Kawasaki Heavy Industries Kabusuki Kaisha), and classified by using a sieve (24 mesh), thereby separating the metal iron from the foamed nickel. The foamed nickel was concentrated to fine particles having 24 mesh or less and recovered.

[0055] On the other hand, the valuables such as nickel hydride and nickel hydroxide acting as active components of the cell were concentrated into the classified material having passed through the sieve of 28 mesh obtained by the wet-crushing and the following classification. The valuables thus obtained were roughly divided into two, such materials mainly composed of the positive electrode and the negative electrode, and the mixture thereof was also prepared.

[0056] Next, the materials recovered from the positive electrode (Examples 1 to 13), from the negative electrode (Examples 14 to 26) and the mixtures thereof (Examples 27 to 32) were subjected to the carbon removing step and the melting step, and amounts of carbon and oxygen in the valuable metals obtained were chemically analyzed.

Example b 1

[0057] After 3 g of the materials recovered from the positive electrode (carbon content and oxygen content were 1.27% in weight and 6.5% in weight, respectively) obtained in the carbon-removing step was subjected to the carbon-removing treatment (carbon-removing step) at 400° C. for one hour while an argon gas was flown at a rate of 200 cc/minutes, the material was further heated at 1400° C. for one hour in the argon atmosphere to be recovered as a melted metal. The carbon content and the oxygen content of the melted metal thus obtained were reduced to 0.93% in weight and 6.5% in weight, respectively. The results are summarized in Table 1.

Examples 2 to 7

[0058] The materials recovered from the positive electrode having substantially same composition as that of Example 1 were subjected to the carbon-removing step at a temperature and a period of time specified in Table 1 while an atmosphere gas was flown, and then was melted with heat under the same condition as those of Example 1 The carbon contents and the oxygen contents in the melted metals obtained by the treatments were shown in Table 1. When the experiment was conducted in the hydrogen atmosphere, the flow gas was replaced with an argon gas after a specified period of time for the reaction of the carbon-removing step and the metal was cooled. “Ar(H₂O)” in Table 1 refers to an argon gas saturated with vapor.

Examples 8 to 13

[0059] materials recovered from the positive electrode having substantially same composition as that of Example 1 were subjected to the carbon-removing step at a temperature and a period of time specified in Table 1 in an atmosphere gas flow and the materials recovered from the positive electrode were rotated (agitated), and then were melted with heat under the same condition as those of Example 1. The carbon contents and the oxygen contents in the materials obtained by the treatments were shown in Table 1. TABLE 1 Temp. Hour Gas and Gas Flow Rotation C Content O Content (° C.) (h) (cc/min.) (rpm) (weight %) (weight %) Positive — — — — 1.27 6.5 Electrode Ex. 1 400 1 Ar-200 — 0.93 4.3 2 400 1 H₂-200 — 0.35 4.1 3 800 1 H₂-200 — 0.21 4.7 4 800 1 Ar(H₂O)-200 — 0.04 6.2 5 1000 1 Ar(H₂O)-200 — 0.05 6.4 6 800 1 Ar(H₂O),H₂-200 — 0.13 6.0 7 1000 1 Ar(H₂O),H₂-200 — 0.04 6.0 8 600 1 H₂-200 10 0.07 2.9 9 800 1 H₂-200 10 0.08 3.2 10 1000 1 H₂-200 10 0.01 2.8 11 600 1 H₂-1000 10 0.11 2.5 12 800 1 H₂-1000 10 0.06 1.9 13 1000 1 H₂-1000 10 0.01 1.9

Observations in Examples 1 to 13

[0060] Judging from the experimental results of Examples 1 to 13, the reduction of the carbon contents and the oxygen contents were confirmed in all the Examples by conducting the carbon-removing step. This shows that part of the carbon in the valuable metal was removed and that the oxygen in the oxidized nickel, cobalt and manganese in the scrapped nickel-hydrogen secondary cell was reduced, and the nickel hydroxide in the negative electrode was hydrolyzed to be converted into nickel oxide which was further reduced to the metal. The amount of the decrease of the carbon increased with the elevation of the temperature so long as the other conditions were the same (excluding Examples 4 and 5). The change of the inert gas atmosphere to the hydrogen gas atmosphere increased the amount of the decrease of the carbon.

[0061] When the carbon-removing step was conducted is without rotation, the carbon content was decreased as low as to 0.04% in weight. The carbon content was further decreased to 0.01% in weight while the valuables were rotated at a temperature of 1000° C. in the hydrogen atmosphere.

[0062] The rate-determining step of the carbon-removing step was the collision between the molecules, and the reduction of the carbon was accelerated by the rotation or the agitation of the materials recovered from the positive electrode to be treated.

[0063] The carbon content of Examples 4 and 5 in the carbon-removing step conducted in the vapor atmosphere decreased to 0.04 to 0.05% in weight. The result shows the vapor will be enough for carbon removal if the purpose is only to remove the carbon from the materials.

[0064] In Examples 1 to 7 in which no rotations were conducted including Examples 4 and 5, the oxygen contents decreased to only about 4% in weight, and those of Examples 4 and 5 were 6% in weight which was a similar level to that of the raw material, and the oxygen decrease was insufficient.

Example 14

[0065] After 3 g of the materials recovered from the negative (carbon content and oxygen content were 0.54% in weight and 22.5% in weight, respectively) obtained in the carbon-removing step were subjected to the carbon-removing treatment (carbon-removing step) at 400° C. for one hour while an argon gas was flown at a rate of 200 cc/minutes, the material was further heated at 1400° C. for one hour in the argon atmosphere to be recovered as a melted metal. The carbon content and the oxygen content of the melted metal thus obtained were reduced to 0.22% in weight and 18.0% in weight, respectively. The results are summarized in Table 2.

Examples 15 to 20

[0066] The materials recovered from the negative electrode having substantially same composition as that of Example 14 were subjected to the carbon-removing step at a temperature and a period of time specified in Table 2 while an atmosphere gas was flown, and then were melted with heat under the same condition as those of Example 14. The carbon contents and the oxygen contents in the melted metals obtained by the treatments were shown in Table 2. When the experiment was conducted in the hydrogen atmosphere, the flow gas was replaced with an argon gas after a specified period of time for the reaction of the carbon-removing step and the metal was cooled.

Examples 21 to 26

[0067] The materials recovered from the negative electrode having substantially same composition as that of Example 14 were subjected to the carbon-removing step at a temperature and a period of time specified in Table 2 while an atmosphere gas was flown and the materials recovered from the negative electrode were rotated (agitated), and then were melted with heat under the same condition as those of Example 14. The carbon contents and the oxygen contents in the melted metals obtained by the treatments were shown in Table 2.

Observations in Examples 14 to 26

[0068] Judging from the experimental results of Examples 14 to 26, similarly to those of Examples 1 to 13, the reduction of the carbon contents and the oxygen contents were confirmed in all the Examples by conducting the carbon-removing step. This shows that part of the carbon in the valuable metal was removed and that the oxygen in the oxidized nickel, cobalt and manganese in the scrapped nickel-hydrogen secondary cell was reduced, and the nickel hydroxide in the negative electrode was hydrolyzed to be converted into nickel oxide which was further reduced to the metal. The amount of the decrease of the carbon increased with the elevation of the temperature so long as the other conditions were the same (excluding Examples 25 and 26). The change of the inert gas atmosphere to the hydrogen gas atmosphere increased the amount of the decrease of the carbon.

[0069] Different from the materials recovered from the positive electrode, the carbon content was decreased to 0.01% in weight in the carbon-removing step even without the rotation. This is because the initial carbon content was small.

[0070] The carbon-removing effect affected by the rotation was not constant, and the remarkable effect did not appear.

[0071] The carbon content was deceased to the order of 0.0-0.02% in weight in the carbon-removing step in the hydrogen gas atmosphere. The oxygen content increased with the temperature rise under the same conditions (excluding Examples 17 and 18), and increased to 0.63% in weight in Example 26. TABLE 2 Temp. Time Gas and Gas Flow Rotation C Content O Content (° C.) (h) Rate (cc/min.) (rpm) (weight %) (weight %) Negative — — — — 0.54 22.5 Electrode Ex. 14 400 1 Ar-200 — 0.22 18.0 15 500 1 H₂-200 — 0.05 2.6 16 800 1 H₂-200 — 0.01 1.1 17 800 1 Ar(H₂O)-200 — 0.16 15.3 18 1000 1 Ar(H₂O)-200 — 0.04 15.8 19 800 1 Ar(H₂O),H₂-200 — 0.18 0.95 20 1000 1 Ar(H₂O),H₂-200 — 0.02 0.66 21 600 1 H₂-200 10 0.14 1.35 22 800 1 H₂-200 10 0.12 1.05 23 1000 1 H₂-200 10 0.03 0.89 24 600 1 H₂-1000 10 0.03 1.25 25 800 1 H₂-1000 10 0.01 0.86 26 1000 1 H₂-1000 10 0.02 0.63

Example 27

[0072] After 3 g of the mixture including the materials recovered from the negative electrode and the positive electrode (carbon content and oxygen content were 0.91% in weight and 16.2% in weight, respectively) obtained in the valuables recovering step was subjected to the carbon-removing treatment (carbon-removing step) at 300° C. for one hour while an argon gas was flown at a rate of 200 cc/minutes, the material was further heated at 1400° C. for one hour in the argon atmosphere to be recovered as a melted metal. The carbon content and the oxygen content of the melted metal thus obtained were reduced to 0.88% in weight and 11.2% in weight, respectively. The results are summarized in Table 3 wherein “+:−” refers to the mixing ratio between the materials recovered from the positive and negative electrodes.

Examples 28 to 32

[0073] The mixture having substantially same composition as that of Example 27 was subjected to the carbon-removing step at a temperature and a period of time specified in Table 3 while an atmosphere gas was flown, and then was melted with heat under the same condition as those of Example 27. The carbon contents and the oxygen contents in the melted metals obtained by the treatments were shown in Table 3.

Observations in Examples 27 to 32

[0074] Judging from the experimental results of Examples 27 to 32, the reduction of the carbon contents and the oxygen contents were confirmed in all the Examples by conducting the carbon-removing step. Especially under the hydrogen gas atmosphere (Example 32), the carbon content and the oxygen content were reduced to 0.01% in weight and 1.1% in weight, respectively. This shows that part of the carbon in the valuable metal was removed and that the oxygen in the oxidized nickel, cobalt and manganese in the scrapped nickel-hydrogen secondary cell was reduced, and the nickel hydroxide in the negative electrode was hydrolyzed to be converted into nickel oxide which was further reduced to the metal It was conjectured that the carbon removal was efficiently carried out by the vapor produced by the hydrolysis.

[0075] Judging from these results, it was elucidated that the carbon content in the valuables could be largely decreased when the mixture including the materials recovered from the positive and negative electrodes was treated in the carbon-removing step during the recovery of the valuable metal from the scrapped cell without separating the mixture. TABLE 3 Temp. Time Gas and Gas Flow C Content O Content (° C.) (h) (cc/min.) +:− (weight %) (weight %) Mixture — — — 1:1 0.91 16.2 Exam- 27 300 1 Ar-200 1:1 0.88 11.2 ple 28 400 1 H₂-200 1:1 0.16 7.4 29 500 1 H₂-200 1:1 0.18 4.2 30 800 1 H₂-200 1:1 0.01 3.7 31 800 1 H₂-200 1:0 0.21 4.7 32 800 1 H₂-200 0:1 0.01 1.1

Valuable Metal Recovering Step

[0076] The valuables thus obtained had the composition of about 60% in weight of cobalt and nickel, about 33% in weight of the Misch metal and about 7% in weight of manganese and aluminum.

[0077] Then, the nickel and the cobalt were recovered from the mixture including the valuables and slag or the mixture including the same composition of the valuables prepared from commercially available metals and slag.

Example 33

[0078] After 5 g of boron oxide acting as a flux component was added to 10 g of a mixture including the valuables obtained in Example 1 and slag, it was heated to 1300° C. in a reaction vessel having an argon atmosphere therein for 30 minutes for proceeding the reaction. Thereby, an upper layer of the melted slag and a lower melted metal appeared in the reaction vessel, and the two layers were separated from each other by decantation.

[0079] After the decantation, 6.1 g of the valuable metal was obtained, and 1.0 g of transparent slag and 0.3 g of other slag were also obtained. The valuable metal was collected as much as possible, but the slag which was basically useless was recovered for analysis and a considerable amount of the slag was not collected. The experimental conditions, and the amounts of the recovered valuable metal and slag were summarized in Table 4.

[0080] The analysis of the recovered valuable metal revealed that the recovered metal included 97% in weight of nickel+cobalt+manganese (the individual composition included 86% in weight of the nickel, 8.4% in weight of the cobalt and 5.4% in weight of the manganese), 3% in weight of the boron, 0.57% in weight of unidentified carbon compounds and 0.02% in weight of unidentified oxygen compounds. The results of the analysis were summarized in Table 5. The recovery and the analysis of most of the slag were not practiced. Such slag is indicated by “−” in Tables 4 and 5. TABLE 4 Yield After Experimental Conditions Reaction (g) Positive Flux Trans- Temp. Time Atmos- Electrode Component parent Other (° C.) (m) phere (g) (g) Metal Slag Slag Exam- 33 1300 30 Ar 10 B₂O₃ (5) 6.1 1.0 0.3 ple 34 1300 30 Ar 10 B₂O₃ (5) 6.7 4.1 — 35 1300 120 Ar 10 B₂O₃ (5) 6.7 3.4 — 36 1300 5 Ar 5 B₂O₃ (1) 3.0 — — 37 1300 5 Ar 5 B₂O₃ (2) 3.0 — — 38 1300 5 Ar 5 B₂O₃ (1) 2.9 — — 39 1300 5 Ar 5 B₂O₃ (2) 2.9 — — 40 1300 5 Ar 5 B₂O₃ —CaO (2) 3.2 — — 41 1300 5 Ar 5 B₂O₃ —CaO (1) 3.0 — — 42 1300 5 Ar 5 B₂O₃ — 2.8 — — CaO (0.5) 43 1300 30 Ar 5 B₂O₃—CaO (3) 3.0 — — 44 1300 30 Ar 5 B₂O₃ (3) 3.2 — — Comp. 1 1300 30 Ar 5 None 0.9 — — Exam- 2 1400 30 Ar 5 None 1.4 — — ple

Examples 34 to 44

[0081] The valuable metals were recovered from the mixture including the valuables and the slag similarly to Example 33 under the conditions specified in Table 4. The results were shown in Tables 4 and 5. TABLE 5 Analytical Value of Recovered Material (weight %) Transparent Metal Slag Other Slag Mm Ni, Co, Mn B C O Mm Ni, Co Mm Ni, Co Exam- 33 0.1 97 3 0.57 0.02 24 0 43 16 ple 34 0 95 5 0.04 0.02 50 2.5 — — 35 0 95 5 0.01 0.02 48 0.5 — — 36 0 99 0.8 0.50 0.16 — — — — 37 0 99 1 0.62 0.03 — — — — 38 0 99 0.9 0.05 0.03 — — — — 39 0 99 0.9 40 0.1 99.4 0.5 0.79 0.03 — — — — 41 0.23 99.4 0.2 0.76 0.04 — — — — 42 0 99.8 0.2 0.72 0.04 — — — — 43 1.2 92.5 4.6 0.03 0.17 — — — — 44 0 94 5.1 0.015 0.01 0.1 — 16 67 Comp. 1 6 94 — 0.51 0.51 0.1 — — — Exam- 2 0 99.7 — — — — — ple

Comparative Examples 1 and 2

[0082] The valuable metals were recovered from the mixture including the valuables and the slag similarly to Example 33 by using no flux component under the conditions specified in Table 4. The results were shown in Tables 4 and 5.

Observations in Examples 34 to 44 and Comparative Examples 1 and 2

[0083] As mentioned before, the metal composition in the valuables obtained from the scrap included about 60% in weight of Ni+Co, about 33% in weight of the Misch metal and about 7% in weight of Mn+Al. Considering that the Misch metal could not be recovered, the theoretical recovery is about 60 to 65% in weight. As apparent from Example 33, except that almost all the Misch metal was mixed into the recovered slag, almost all the metal could be recovered as the melted valuable metals because the other metals such as the nickel was not mixed into the slag. The recovering amount per 10 g of the positive electrode was 5.6 to 6.7 g which was nearly to the theoretical value. Accordingly, the valuable metals could be recovered almost quantitatively by means of the valuable metal recovering step in which the flux component was added.

Examples 45 to 52 and Comparative Example 3

[0084] Similarly to Example 33, the mixture of the valuables and the slag added with or without boron oxide was heated and reacted in a reaction vessel having an argon atmosphere therein under the experimental conditions specified in Table 6. The valuable metals, transparent slag and other slag were obtained in yields shown in Table 6, and subjected to the ICP analysis. The results of the analysis were shown in Table 7. TABLE 6 Yield After Experimental Conditions Reaction (g) Positive Flux Trans- Temp. Time Atmos- Electrode Component parent Other (° C.) (m) phere (g) (g) Metal Slag Slag Exam- 45 1300 30 Ar 2.5 B₂O₃ (5) 1.34 1.53 1.37 ple 46 1300 30 Ar 5 B₂O₃ (5) 2.41 0.80 0.16 47 1300 30 Ar 7.5 B₂O₃ (5) 4.23 1.61 0.29 48 1300 30 Ar 10 B₂O₃ (5) 6.11 1.02 0.30 49 1300 30 Ar 15 B₂O₃ (5) 8.69 3.15 — 50 1300 30 Ar 10 B₂O₃ (10) 3.71 3.21 — 51 1300 30 Ar 10 B₂O₃ (5) 6.67 4.06 — 52 1300 120 Ar 10 B₂O₃ (5) 6.66 3.43 — * 3 1300 30 Ar 5 None 0.87 — —

Examples 53 to 63 and Comparative Examples 4 and 5

[0085] Similarly to Example 33, the mixture of the valuables and the slag added with or without boron oxide was heated and reacted in a reaction vessel having an argon atmosphere therein under the experimental conditions specified in Table 8. The valuable metals, transparent slag and other slag were obtained in yields shown in Table 8. TABLE 7 ICP Analysis Results (weight %) La Ce Nd Pr Ni Mn Al Co B Ga ToThl C O Valuable Metal Example 45 0.0 0.0 0.0 0.0 89.0 0.9 0.0 0.0 98.7 0.81 0.02 46 0.0 0.0 0.0 0.0 89.0 2.4 0.0 0.0 100.1 0.51 0.02 47 0.0 0.0 0.0 0.0 86.0 4.1 0.0 0.0 3.3 98.6 0.51 0.05 48 0.1 0.0 0.0 0.1 88.0 5.4 0.0 0.1 103.2 0.57 0.02 49 0.0 0.0 0.0 0.0 84.0 3.5 0.0 0.0 100.1 0.36 0.04 50 0.0 0.0 0.0 0.0 89.0 4.3 0.0 0.0 0.0 96.0 0.11 0.03 51 0.0 0.0 0.0 0.0 82.0 6.6 0.0 0.0 5.3 110.9 0.04 0.02 52 0.0 0.0 0.0 0.0 85.0 6.2 0.0 0.0 5.3 114.5 0.01 0.02 * 3 1.4 4.0 1.1 0.3 84.0 8.7 4.0 8.7 0.1 112.4 0.51 0.02 Transparent Slag Example 45 14.0 7.0 2.2 0.7 0.0 3.4 11.0 0.0 15.0 53.3 0 22.3 46 20.0 9.4 2.9 1.0 0.2 4.1 11.0 0.0 12.0 60.6 0.02 22.3 47 24.0 12.0 3.5 1.1 0.0 3.4 9.8 0.0 10.0 63.8 0.03 22.3 48 26.0 13.0 3.9 1.2 0.1 2.7 9.2 0.0 9.3 65.4 0.07 22.3 49 24.0 12.0 3.6 1.1 0.1 3.9 10.0 0.0 9.7 64.4 0.06 *** 50 11.0 5.0 1.6 0.5 0.5 0.9 7.4 0.1 14.0 17.0 57.9 0.04 *** Other Slag Example 45 2.1 0.9 0.3 0.1 0.4 0.6 2.7 0.0 28.0 35.1 0.02 *** 46 12.0 5.5 1.7 5.8 29.0 3.1 6.2 3.0 10.0 76.4 ** *** 47 4.6 2.3 0.7 0.2 3.6 1.2 3.4 0.4 23.0 39.5 0.23 *** 48 26.0 12.0 3.7 1.4 7.4 3.2 8.0 0.8 8.6 71.1 1.21 *** 49 16 24 7.3 2.2 2.2 2.6 9.1 0.26 8.6 72.26 0.08 *** 50 16 23 7.2 2.2 0.41 2.4 9.8 0.07 8.8 69.88 0.05 ***

[0086] Since the above embodiments are described only for examples, the present invention is not limited to the above embodiments and various modifications or alternations can be easily made therefrom by those skilled in the art without departing from the scope of the present invention. TABLE 8 Yield After Experimental Conditions Reaction (g) Positive Flux Trans- Temp. Time Atmos- Electrode Component parent Other (° C.) (m) phere (g) (g) Metal Slag Slag Exam- 53 1300 5 Ar 5 B₂O₃ (1) 3.0 — — ple 54 1300 5 Ar 5 B₂O₃ (1.5) 2.9 — — 55 1300 5 Ar 5 B₂O₃ (2) 3.0 — — 56 1300 5 Ar 5 B₂O₃ (1) 2.9 — — 57 1300 5 Ar 5 B₂O₃ (1.5) 2.9 — — 58 1300 5 Ar 5 B₂O₃ (2) 1.6 — — 59 1300 5 Ar 5 B₂O₃—CaO (2) 3.2 — — 60 1300 5 Ar 3 B₂O₃—CaO (1) 3.0 — — 61 1300 5 Ar 5 B₂O₃— 2.8 — — CaO (0.5) 62 1300 30 Ar 5 B₂O₃—CaO (3) 3.0 — — 63 1300 30 Ar 5 B₂O₃—CaO (3) 3.2 — — * 4 1400 30 Ar 5 None 1.4 — — 5 1300 30 Ar 3 None 1.1 — — 

What is claimed is:
 1. A method for recovering a valuable metal comprising the steps of: recovering valuables from scraps containing the valuable metal; and removing at least part of carbon contained in the recovered valuables by heating the valuables in a non-oxidizable atmosphere.
 2. The method as defined in claim 1 , wherein the scraps containing the valuable metal are a scrapped nickel-hydrogen secondary cell.
 3. The method as defined in claim 1 , wherein the valuables are selected from the group consisting of materials recovered from a positive electrode, materials recovered from a negative electrode and a mixture thereof.
 4. The method as defined in claim 1 , wherein the non-oxidizable atmosphere is selected from the group consisting of an inert gas atmosphere, a hydrogen gas atmosphere, a vapor atmosphere, an inert gas-vapor atmosphere and an inert gas-vapor-hydrogen gas atmosphere.
 5. The method as defined in claim 1 , wherein the heating in the carbon-removing step is conducted at a temperature between 350 and 1050° C. for 5 minutes to 10 hours
 6. The method as defined in claim 1 , wherein the heating in the carbon-removing step is conducted while the valuables are stirred.
 7. The method for recovering the valuable metal as defined in claim 1 further comprising the step of heating the recovered valuable metal for melting.
 8. A method for recovering a valuable metal comprising the steps of: thermally treating a melted mixture including the valuable metal and slag with a flux component to separate the valuable metal in a liquid phase from the slag in another liquid phase.
 9. The method for recovering the valuable metal as defined in claim 8 , wherein the flux component is boron oxide.
 10. The method for recovering the valuable metal as defined in claim 8 , wherein the flux component is a mixture containing boron oxide and calcium oxide.
 11. A method for recovering a valuable metal comprising the steps of: recovering valuables from scraps containing the valuable metal and slag; removing at least part of carbon contained in the recovered valuables by heating the valuables in a non-oxidizable atmosphere to provide a melted mixture including the valuable metal and the slag; and thermally treating the melted mixture with a flux component to separate the valuable metal in a liquid phase from the slag in another liquid phase. 